The waveform received at a radio receiver (e.g. an FM or DAB receiver) may be described in terms of its in-phase (I) and quadrature (Q) components and within a receiver there may be separate paths for each of the I and Q components. In a receiver where the I and Q paths are not exactly balanced in both amplitude and phase, the resulting IQ imbalance causes a signal at frequency F to suffer interference from its mirror image at frequency −F and it is not possible to filter out this interference because the interference occurs at the same frequency as the signal itself. Unless the IQ imbalance or the resulting interference is corrected, the interference results in an increase in the error rate of the receiver. The effect of any IQ imbalance increases for higher order modulation schemes, (e.g. QPSK or 16-QAM).
A known way of calculating the IQ amplitude imbalance is to measure the amplitude of both the I and Q components and then to take the difference between the two values. This difference can then be used to correct for the IQ amplitude imbalance.
The embodiments described below are not limited to implementations which solve any or all of the disadvantages of known receivers (e.g. radio, TV and WiFi™ receivers).